It's measured by subsequent performance in the amount by which the winner wins equals the amount by which the loser loses, but it costs a lot to play the game.

之后的业绩表现可判输赢,而且赢方赚的钱,就等于输方赔的钱,但是交易本身会产生巨大的成本

耶鲁公开课 - 金融市场课程节选